Material Damping of Crushed Rock in Free-Decay Mode

Damping of geo-materials in resonant column test is commonly evaluated with two alternative experimental methods; during a steady-state vibration (SSV) and during free-vibration decay (FVD). Damping is an important dynamic property necessary to capture the complete behavior of soils. In the study, representative test results on crushed rock are discussed with a focus on material damping derivations along with stiffness degradation test results derived from torsional resonant column tests. A comparison between material damping derived from the SSV and FVD methods and from small to medium shear strains is presented and discussed. In the first part of the paper, the definition of material damping by means of a closed loop in the shear stress - shear strain plane is presented along with a report on literature data associated with damping of coarse-grained soils and the important factors that control material damping of sands and gravels. In the second part, the materials and experimental techniques of the study are described briefly and the background of determining material damping in a resonant column test is also presented along with the analytical formulae. Finally, in the third part representative test results are given including both stiffness and damping, and a comparison of damping derivations using different methods is also highlighted.